The present invention is related to an apparatus for coding data to record coded data on a recording/reproducing apparatus for reproducing and decoding the recorded data. More specifically, the present invention is directed to a method for coding and decoding data.
To understand the present invention, the conventional technique will be briefly explained. The conventional technique involves explanations about the Viterbi algorithm and trellis representation, the partial response channel, and the error correction.
The Viterbi algorithm is to determine a most likelihood path along branches of a trellis diagram. The respective branches of the trellis diagram are weighted with respect to the values of input signals. The Viterbi algorithm may determine such a path for constituting the most likelihood degree based upon the accumulated value of these weighted values.
A so-called “PRML (Partial Response Maximum Likelihood) system” is widely used in magnetic recording/reproducing apparatuses. In this PRML system, the partial response (PR) channel is combined with this Viterbi algorithm. A system polynomial known as the partial response class 4 (PR4) is expressed by G(D)=(1−D)(1+D), assuming now that symbol “D” is a delay operator. Furthermore, with respect to high density recording operations, it is known that the extended partial response class 4 (EPR4), the extended EPR4 of G(D)=(1−D) (1+D)3, and the MEEPR4 (Modified Extended EPR4) of G(D)=(1−D2) (5+4D+2D2) are suitably employed. The extended partial response class 4 is expressed by a higher-order of G(D)=(1−D) (1+D)2.
As the system capable of suppressing an occurrence of such an error, and the method for improving the decoding performance, the following idea is conceivable. In this decoding performance improving method, the errors which occur at the same time are locally corrected. That is, as described in the publication entitled “A New Target Response with Parity Coding for High Density Magnetic Recording Channels” written by Thomas Conway (IEEE Transactions on Magnetics, Vol. 34, No. 4, July 1998), the parity bit is added to the code word when the data is recorded, whereas the error detection/correction are carried out when the data is read. For example, the minimum distance decoding error in the extended EPR4ML is the 3-bit continuous error. Such an odd-numbered bit error can be detected during the reproducing operation by adding a 1-bit parity bit thereto.